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II CORE BLOCK: INITIAL RESET
S1C33L03 FUNCTION PART EPSON B-II-3-1
A-1
B-II
Reset
II-3 INITIAL RESET
Pins for Initial Reset
Table 3.1 shows the pins used for initial reset.
Table 3.1 Pins for Initial Reset
Pin name I/O Function
#RESET I Initial reset input pin (Low active)
Low: Resets the CPU.
#NMI I NMI request input pin
This pin is also used for selecting a reset method.
High: Cold start
Low: Hot start
The chip is reset when the #RESET pin goes low and starts operating at the rising edge of the reset signal. The
CPU and internal peripheral circuits are initialized while the #RESET pin is low.
Cold Start and Hot Start
The CPU supports two initial reset methods: cold start and hot start. The #NMI pin is used with the #RESET pin to
set this condition.
The differences between cold start and hot start are shown in Table 3.2.
Table 3.2 Differences between Cold Start and Hot Start
Setup contents Cold start Hot start
Reset condition #RESET = low & #NMI = high #RESET = low & #NMI = low
CPU: PC The vector at the boot address is loaded to the PC.
CPU: PSR All the PSR bits are reset to 0.
CPU: Other registers Undefined
CPU: Operating clock The CPU operates with the OSC3 clock.
External bus status (0x48120–0x4813F) Initialized Status is retained.
Oscillation circuit Both the OSC1 and OSC3 circuits start oscillating.
I/O pin status (0x402C0–0x402DF) Initialized Status is retained.
Other peripheral circuit Initialized or undefined
Since cold start initializes all the internal peripheral circuits as well as the CPU, it is useful as a power-on reset.
Hot start initializes the CPU and peripheral circuits, but does not reset the bus control unit and the input, output and
I/O port status. It is therefore useful as a reset that maintains the external bus and I/O pin status during operation.
The #NMI pin that specifies the reset method should be set following the timing chart shown in Figure 3.1.
(1) Cold start (2) Hot start
#NMI
#RESET
Cold start is generated
(#RESET = low & #NMI = high)
#NMI must be set to high longer than
the reset pulse width.
#NMI
#RESET
Hot start is generated
(#RESET = low & #NMI = low)
#NMI must be set to low longer than
the reset pulse width.
Figure 3.1 Setup of #RESET and #NMI Pins